Most drums have one or two skins (heads) and a shell between them. The heads are usually struck with hands, fingers, sticks or mallets. Other than the human voice, percussion instruments are the oldest form of musical instruments. Drums are percussion instruments, sometimes classified as membranophones.
There are innumerable types of drums originating from right across the world. However, drums are usually classified according to two things: the type and method of attaching the skin, and the shape of the shell. The first of these helps to differentiate between modern and traditional or more primitive instruments, whose heads may be simply affixed to the shell with strings, ropes and nails. Sometimes pegs are placed within the strings and twisted in order to apply extra tension to the head. African Talking Drums have cords that are squeezed by the players arm to vary the pitch of the drum. The more modern method of head tensioning uses hoops, brackets and screws. The modern snare drum uses hoops that hold the collar of the drumhead which are attached to lug brackets fixed to the shell. The pitch is raised by tightening the head; conversely, to lower the pitch the head should be loosened.
Drumheads can be made from animal hide, fish skin, cloth or synthetic materials. The shell functions as a resonating chamber that amplifies the volume as well as affecting the timbre of the instrument.
Its shape can affect timbre; common drum shapes include the cylinder, cone, barrel, hemispheric, parabolic, box and gourd shaped drums. Combinations and variations are commonplace. The Conga is similar in shape to a barrel and their stave construction further indicates that early drums may have actually been made from salvaged barrels.